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Myths abound on correct tire inflation


An executive of Drivers.com recently bought four used tires from a dealer and was told to keep the pressure four psi (pounds per square inch) higher in winter than in summer. Not so.

Reader's comments below

At a time when tires are making the headlines every day because of the Firestone controversy, this anecdote only serves to illustrate how much misinformation is circulating about tires and their care and maintenance.

Other myths about tire inflation include keeping the pressure lower in winter than in summer; and that the best time to check tire pressure is after a long trip.

In fact, tire pressure usually lowers itself in winter and raises itself in summer-it requires no action on the part of the motorist apart from keeping the pressure at the level recommended on the sticker that is usually located just inside the door, glove box, or fuel door. Under normal loads, inflate tires according to the vehicle manufacturer's recommendations, NOT the maximum pressure listed on the sidewall. In any case, one should never exceed this maximum pressure.

The sidewall, incidentally, also shows the type of cord and number of plies in the sidewall and under the tread.

Every time the outside temperature drops 10 degrees Fahrenheit, the air pressure inside your tires goes down about one or two psi. Drivers should check their tire pressures frequently during cold weather, adding enough air to keep them at recommended levels of inflation at all times.

Another winter no-no, according to the tire experts, is never reduce tire pressures in an attempt to increase traction on snow or ice. It does not work and your tires will be so seriously under-inflated that driving will damage them.

One of the warnings issued by Bridgestone/Firestone and Ford after it was revealed that defective tires may be linked to as many as 88 deaths and 1,400 crashes was that under-inflated tires are likely to overheat and burst. So, if there's any silver lining to these tragedies, it's that they've drawn attention to a potentially deadly traffic hazard.

However, it's important to get the facts straight.

An invaluable resource in this respect is the Tire Industry's Safety Council, which publishes a free 18-page brochure on the latest in tire care. This brochure has safety information for cars and light trucks, including information on proper tire inflation, safety warnings, tire rotation, vehicle conditions affecting tires, speed ratings, replacement tire selection, and tips on cold weather driving. The information is also available on the council's web site.

Among the many useful hints and tips, the council recommends that drivers have their own pressure gauge. "Tires must be properly inflated," the council says. "Use an accurate tire pressure gauge to determine your tire pressure. You can't tell when tires are 'low,' or under-inflated, just by looking. Air meters at service stations may be inaccurate due to exposure or abuse. You should have your own personal tire gauge to be sure."

The council also advises drivers to check their tire inflation pressure (including the spare) at least once a month, and before every long trip.

"Tires must be checked when they are cold; that is, before they have been run a mile. If you must drive over one mile for air, before you leave home, measure the cold inflation pressure of each tire and record the actual under-inflation amount for each tire.

"Upon arriving at the service station, measure each tire's inflation again and then inflate the warm tire to a level that is equal to this warm pressure, plus the cold under-inflation amount."

Tires lose air normally through the process of permeation, the council says. "Changes in outdoor temperature can affect the rate at which your tire loses air. This change is more pronounced in hot weather. Generally speaking, a tire will lose one or two pounds of air per month in cool weather, and even more in warmer weather. Under-inflation is the leading cause of tire failure, so check inflation pressure regularly.

"Never "bleed" or reduce air pressure when tires are hot. It is normal for pressure to build up as a result of driving.

"Make sure all tire valves and extensions are equipped with valve caps with rubber gaskets to keep out dirt and moisture. Have a new valve stem assembly installed whenever a tire is replaced.

"Under-inflation or overloading creates excessive heat," the council warns, "and can lead to tire failure, which could result in vehicle damage and/or serious injury or death. Proper inflation extends tire life and saves fuel."

In North America, regulations require tire manufacturers to grade passenger car tires based on three performance factors: treadwear, traction, and temperature resistance.

The treadwear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test track. A tire graded 200, for example, would wear twice as long on the government test course under specified test conditions as one graded 100.

It is wrong to link treadwear grades with your projected tire mileage. The relative performance of tires depends upon the actual conditions of their use and may vary due to driving habits, service practices, differences in road characteristics, and climate.

Traction grades, from highest to lowest, are A, B, and C. They represent the tire's ability to stop on wet pavement as measured under controlled conditions on specified government test surfaces of asphalt and concrete.

The temperature grades, from highest to lowest, are A, B, and C. These represent the tire's resistance to the generation of heat.

Related links:

Reader's Comment

Bob Joynt:
As an instructor and owner of Control Driving Skills in Smiths Falls, Canada, our classes are taught to keep their tires at the "Maximum" air pressure indicated on the sidewall at all times for safety and vehicle control reasons.... more

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All Comments (22)

Showing 1 - 22 comments

dmw,

My mercedes estate (station wagon) handbook say's something very interesting about pressures and backs up what I've found elsewhere.

The manufacturers stated pressures should be regarded as minimum inflation pressures.

The tyre sidewall should be regarded as maximum inflation pressures.

My handbook says (I paraphrase): if you have to carry a heavy load and so have your tyre pressures increased to the high load levels, when you unload, it is safe to drive on without reducing the pressures, although ride comfort and tyre wear pattern will be comprimised.

Note this difference in pressure is up to an additional 50% pressure (30psi to 45psi) on my car.

Ross Young,

Bob's comment seems little silly in that the tire would then have less traction and stability due to the tire being over inflated based on vehicle weight and give less tired to road contact along with wearing the tire out at a faster rate in the middle of the tread due to this.

rick,

I feel thet the door pressure recomendatio is too soft a ride

Craig,

should the tires be maximum psi before going on a trip with 4 adults and trunk and car top carrier loaded with luggage?

Hmmm,

This can't be right. The pressure while driving is what's important, and the temperature while driving is higher from friction than the temperature standing still. I'd bet the temperature while driving is similar in winter and summer. Measuring the pressure after a long trip seems like the best method. What are your references? Are you spreading myths yourselves?

pictsidhe,

Location makes no difference, unless you are talking about which car it is on. There is no universal pressure for any tyre, it depends what it is fitted to.

Jim Zachary,

What should the cold air pressure for a 225/60R16 tire in Indiana?

Aaron,

The number that you read on the sidewall of the tire is the air pressure that is required if you are at the maximum GCVW stated on the sidewall. For example for an LT265/75R16 LRE or 10 ply rating, you would need to inflate each tire to 80psi if your gross combined vehicle weight (GVWR) was 13,660 lbs or 3,415 per tire. Most people do not carry that much weight that use those tires on their SUVs or pick ups. To find the proper air pressure for the load that you are placing on your tires, you would first need to know how much your total vehicle weight is and then use a load and inflation table like the one found at marktg.toyotires com . The easiest and most convenient way is to contact your local, reputable tire dealer.

Ozzy,

Ok, I have a question! I am dealing with trucks (ie - SUVs and 5th wheels)I see many people who put a little bigger tires than normal on their vehicles. We have a lot of farm vehicles around here and they do a number of jobs, so they need something in a 10 ply or more, but the guys are still saying they run 30 psi in a tire that the maximum is 60 or 80 lbs. What is the rule here? Is there a percent under the tire listed amount to run or a set amount?

Tireman,

35psi is pretty much the norm for most American automobiles.

moonpie1016,

You say to follow the manufacturer pressure for tires...if this is true...what happens when a tire holds less pressure than the auto recommends? I was always taught to go by the sidewalls....but NOT to inflate to top pressure on the tire...and my tires have always lasted MORE than the manufacturers specs....am i wrong?

derkee,

okay, its easier than you think! first AIR does NOT 'shrink'! Freezing is the base point for temperatures. so, in onset of the cold temperatures, the air is becoming less 'EXPANSIVE'. meaning more 'cold' molecules gather in the same cubic area because the 'WARMER' air has(forced by nature), moved south. so, less heat, less expansion of the air, less tire pressure. (always check and add air within +/- ~1000 ft~ elev. 1000ft+about 1psi)

as for the tire pressure, do as i do, pay attention to the weather and plan ahead. IF YOU HAVE TIME, CHECK AND FILL EVERY/OTHERDAY! during 'colder' temperatures, ALL engines perform better but with less MPGs.

1psi low can be as much as 1- MPGs. 3-4psi can be more than 3-4 MPGs. so do the math, 12k miles per year, avg of 2MPGs loss, $2pg= (depending on MPGs,) $100-over $1000 per year. if you have the money to burn and still have some left over to buy a new OZONE layer, than dont bother, however, my savings i apply to gas, maintenance, or insurance.

dorkus1@aol.com,

where on the internet can I find the proper iflation for a 1986 monte carlo?

DK,

Shayne, the air shrinks in cold weather so you need to put more pressure

Shayne Malone,

Why does mt ford say to check tire pressure when its cold out. Summer was fine, did not say anything about my tires in the computer system. All of a sudden when winter hits, it says check pressure...do I ignore this warning light because I know its due to cold weather?

Thank you
Shayne

MP,

Look in your car's owner manual for the recommended tire pressure, and ADD 2 pounds. The factory recommended pressure is for rider comfort and it is suggested to add 2 pounds to that number to get the best gas mileage. Regardless of season, it is advisable to check your tire pressure at the very least once a month, once every two weeks would be even better. Tires lose pressure with changes in temperature and remember always check the pressure when the tires have NOT been driven on for at least 3 hours as you won't get an accurate reading have you recently driven. There really is no minimum tire pressure, as you should always have tires properly inflated. I personally recommend to try to prevent your tires from going more than 5 pounds below the recommended pressure. I also recommend buying a digital tire pressure gauge for about $15. These tend to be more accurate than analog gauges and are worth the price to avoid guessing on analog dials. I also recommend buying a portable air compressor/inflator, which run about $20-$40 depending on model so you have the convenience of inflating your tires at home.

Riley,

Ummm, no, do not go by what is stated on the tire. Always keep your tires at the recommended pressure given by the cars manufacturer. This can be found in the glove box, or on the drivers door sill. The maximum tire pressure stated by the manufacture of the car, NOT THE TIRE, is the pressure that should be run. Phone the dealership that sells the same brand of car you are driving if you can not find the sticker on your car.

DK,

it should be on the tire itself

Dot,

What is the correct tire pressure for a 2001 Pontiac Grand Am? The door panel gives the maximun tire pressure but, what is the minimum tire pressure?

Jennifer,

I have an 1988 Oldsmobile Cutlass Ciera and I want to know what the correct tire pressure is (summer and winter).
Please respond to mrsjfitzgerald@yahoo.com

Thank you

nate,

so is the winter tire inflation different from what the recommended pressure is?

Ileana,

What is the correct pressure for a 225 60 R16 tire. Please respond to pattymonge@hotmail.com.
Thank you


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